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  • 1990-1994  (5)
  • 1
    Electronic Resource
    Electronic Resource
    Elastic properties of the titin filament in the Z-line region of vertebrate striated muscle (1993)
    Springer
    Journal of muscle research and cell motility 14 (1993), S. 416-422 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The characteristics of the titin filament in the vicinity of the Z-line were investigated using immunoelectron microscopy. We used monoclonal titin antibodies T-11 and T-12 on single fibres of frog skeletal muscle, and on Z-line-extracted fibres. It is well established that the I-band region of titin is elastic. We find, however, that the elastic properties are not uniform. The T-12 epitope, which binds near the Z-line at the N1-line level, hardly changes position relative to the Z-line as the sarcomere is stretched. This demonstrates the functional inextensibility of the N1-Z-line region. After extreme stretch (above 6-μm sarcomere length), this zone finally does elongate; thus, the titin molecule in this region is intrisically elastic. The functional inextensibility seen at shorter sarcomere lengths may, therefore, be a result of binding of titin to the actin filament in the zone near the Z-line. When the Z-line was extracted, the T-12 epitope remained in the same position as in the unextracted fibres; it did not retract from the Z-line. Failure to retract implies that functional anchoring of titin is not exclusive to the Z-line, but includes some site closer to the A-band. Combined with the results of the above-mentioned stretch experiment, this result implies a likely binding of titin to the thin filament either focally at the N1 line or all along the entire N1-Z region. Thus, this region of titin is functionally stiff, but intrinsically elastic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00121293
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  • 2
    Electronic Resource
    Electronic Resource
    Filament lengths in frog semitendinosus and tibialis anterior muscle fibres (1993)
    Springer
    Journal of muscle research and cell motility 14 (1993), S. 167-172 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In frog semitendinosus muscle the descending limb of the length-tension curve is shifted rightward relative to that of tibialis anterior. Both the plateau right corner and the zero-force intercept are equally shifted. To investigate the reason for this shift, we compared filament lengths in the two muscles. Single fibres were mechanically skinned, stretched to reveal filaments clearly, incubated in a solution containing one of several antibodies to enhance filament visualization, and examined by electron microscopy. We found no differences of filament length. Thick filament lengths were 1.62 and 1.61 μm, respectively. I-segment lengths were measured by two methods. With the first, filament length was the same for both muscles, 1.95 or 1.98 μm, depending on the value taken for the troponin repeat; with the second it was 1.92 and 1.94 μm, respectively, for the two muscles. These differences are insignificant. Thus, the reported differences of shape of the length-tension curve are not explainable in terms of differences of filament length.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00115451
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  • 3
    Electronic Resource
    Electronic Resource
    Active tension generation in isolated skeletal myofibrils (1993)
    Springer
    Journal of muscle research and cell motility 14 (1993), S. 498-510 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Single or double myofibrils isolated from rabbit psoas muscle were suspended between a fine needle and an optical force transducer. By using a photodiode array, the length of every sarcomere along the specimen could be measured. Relaxed specimens exhibited uniform sarcomere lengths and their passive length-tension curve was comparable to that of larger specimens. Most specimens could be activated and relaxed four to five times before active force levels began to decline; some specimens lasted for 10–15 activation cycles. Active tension (20–22°C) was reproducible from contraction to contraction. The contractile response was dependent on initial sarcomere length. If initially activated at sarcomere lengths of ≥2.7 μm, one group of sarcomeres usually shortened to sarcomere lengths of 1.8–2.0 μm, while the remaining sarcomeres were stretched to longer lengths. Myofibrils that were carefully activated at shorter initial sarcomere lengths usually contracted homogeneously. Both homogeneous and inhomogeneous contractions produced high levels of active tension. Calcium sensitivity was found to be comparable to that in larger preparations; myofibrils immersed in pCa 6.0 solution generated 30% of maximal tension, while pCa 5.5–4.5 resulted in full activation. Active tension at full overlap of thick and thin filaments ranged from 0.34 to 0.94 N mm-2 (mean of 0.59 N mm-2±0.13 sd. n=65). Even allowing for a maximum of 20% nonmyofibrillar space in skinned or intact muscle fibres, the mean tension generated by isolated myofibrils per cross-sectional area is higher than by fibre preparations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00297212
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  • 4
    Electronic Resource
    Electronic Resource
    Contraction-induced movements of water in single fibres of frog skeletal muscle (1993)
    Springer
    Journal of muscle research and cell motility 14 (1993), S. 573-584 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Although X-ray diffraction measurements imply almost constant filament separation during isometric contraction, such constancy does not hold at the level of the isolated cell; cell cross-section increases substantially during isometric contraction. This expansion could arise from accumulation of water drawn from other fibre regions, or from water drawn into the cell from outside. To distinguish between these hypotheses, we froze single fibres of frog skeletal muscle that were jacketed by a thin layer of water. Frozen fibres were freeze-substituted, sectioned transversely, and examined in the electron microscope. In fibres frozen during contraction, we found large amounts of water just beneath the sarcolemma, less in deeper regions, and almost none in the fibre core. Such gradients were absent or diminished in fibres frozen in the relaxed state. The water was not confined to the myofibril space alone; we found large water spaces between myofibrils, particularly near mitochondria. Accumulation of water between myofibrils and around mitochondria implies that the driving force for water movement probably lies outside the filament lattice, and may therefore be osmotic. The fact that the distribution was nonuniform-highest near the sarcolemma and lowest in the core-implies that the water was likely drawn from the thin jacket surrounding the cell. Thus, the contractile cycle appears to be associated with water entry into and exit from the cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00141554
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  • 5
    Electronic Resource
    Electronic Resource
    Elastic properties of titin filaments demonstrated using a “freeze-break” technique (1993)
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 24 (1993), S. 274-283 
    Details
    ISSN: 0886-1544
    Keywords: immunoelectron microscopy ; rabbit psoas ; elasticity ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A “freeze-break” technique (Trombitás, K.: Acta Biochim. Biophys. Hung. 6:419-427, 1971) and immunoelectron microscopy were used to study the elastic properties of titin filaments. Small bundles of freshly prepared rabbit psoas muscle fibers were quickly frozen and broken under liquid nitrogen to fracture sarcomeres in planes perpendicular to the filament axis, in each of various regions along the sarcomere. The still-frozen specimens were thawed during fixation to allow elastic filaments to retract. The broken specimens were then labelled with monoclonal anti-titin antibodies against an unique epitope in the I-band.The titin epitopes were normally positioned symmetrically about the Z-line. However, in sarcomeres broken at the A-I junction, the epitopes no longer remained symmetrical: the titin filaments in the broken half-sarcomere retracted, independently of the thin filaments, forming a dense band just near the Z-line. The retracted density apparently did not reach the Z-line; retraction stopped at the level of the so-called N1-line. In sarcomeres broken at the Z-line level, the titin filaments retracted in the opposite direction. In this case the titin epitope retracted all the way to the ends of the thick filaments.It appears then that titin molecules form elastic filaments that are independent of thin filaments in most of the I-band. Near the Z-line, however, the titin filaments either have an inelastic domain or associate firmly with the thin filaments at the N1-line level. © 1993 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cm.970240408
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